1. Field of the Invention
This invention relates generally to a seat, and, more particularly, to a seat with a pair of moving seat platforms.
2. Description of the Related Art
Most seats in the past did not promote occupant movement. Seats that do not promote occupant movement cause the seated occupant to sit in a constrained or static posture. This can lead to a number of health-related problems. For example, constrained occupant seating postures can cause joint impairments (arthritis), inflamed tendon sheaths (tendinitis, peritendinitis), chronic joint degeneration (arthroses), and muscle pain (e.g., when the occupant shifts weight on the seat bones, from side to side, or leans to one side, the occupant stresses his or her back muscles to remain adequately supported on the seat).
Prolonged static seating has also been linked to back problems because of the prolonged static pressure on the spine. Prolonged static pressure on the spine impairs fluid flow from the discs, impairing glucose transport, disc nutrition, and the elimination of waste products.
Constrained occupant postures also cause poor circulation. Edema of the lower legs is commonly induced by lack of movement. Leg edema is problematic because local pooling of the blood increases venous pressures to the heart, blood pressure, and heart rate. Edema may predispose the occupant to varicose veins, hemorrhoids, and other peripheral venous disorders such as cold feet. Another circulation problem resulting from seats that do not promote occupant movement is deep venous thrombosis caused by the formation of venous clots in the legs. These blood clot formations occur from sitting in a static position for long periods of time. Other circulation problems occur when certain parts of the occupant""s posterior or legs experience greater pressure than the other seated portions of the occupant. This occurs when a portion of the seat, especially the front, digs into the posterior or legs of the occupant, or if the occupant leans more towards one side of the seat than the other. These concentrated forces on the legs and posterior inhibit circulation and lead to discomfort.
Some seats have been designed to promote occupant movement and improve the comfort of the seated occupant. Some of these seats include a pair of seat platforms that move independently of each other. Each seat platform rocks in a see-saw manner on a fulcrum. In one of these seats, the fulcrum also allows vertical movement of the seat platform as the seat platform slides backwards and forwards. The independent seat platforms are designed to be self aligning, and allow the posterior of the occupant to move normally and independently without restraint, improving seat comfort.
The problem with these seats is that they are not comfortable for multiple seating applications and environments (e.g., office, home, automobile, etc.). In most seating environments, these seats do not properly distribute the weight of the body being borne by the ischial tuberosities (xe2x80x9cseat bonesxe2x80x9d) and the residual weight of the posterior and thigh over the two seating platforms during different seat positions (e.g., one leg up, both legs up, both legs down, legs crossed, etc.). This causes discomfort and circulation problems. Also, in most seating environments, the seats did not allow the exercise necessary for the muscles, tendons, and ligaments of the lower back, pelvis, and thigh areas. This leads to circulation problems, flexibility problems, and back problems.
An object of the present invention is to overcome the above-described difficulties of static seating.
An aspect of the present invention involves the recognition that in a seat with a pair of moving seat assemblies, optimal seating comfort is achieved by providing the seat assemblies at a predetermined neutral angle appropriate for the particular application of the seat. The neutral angle is defined as the angle, relative to horizontal, at which the seat assemblies are initially oriented before external forces are applied to the seat. It is further recognized that each seat assembly should rock and move vertically up to a predetermined amount corresponding to the neutral angle.
Another aspect of the present invention involves four additional recognitions. First, in greater positive neutral angle seating applications (leaned-back seating), the amount of rocking and vertical movement should be greater. Second, in smaller positive neutral angle seating applications, the amount of rocking and vertical movement should be smaller. Third, in greater negative neutral angle seating applications (leaned-forward seating), the amount of rocking movement should be greater, but the amount of vertical movement should be smaller. Finally, in smaller negative neutral angle seating applications, the amount of rocking and vertical movement should be smaller.
An additional aspect of the present invention involves a seat with a pair of moving seat assemblies. A motion mechanism allows vertical motion and rocking motion in each seat assembly. The seat assembly is provided at a neutral angle based on the application of the seat. The total amount of rocking motion and vertical motion allowed depends on the neutral angle of the seat assembly. This combination causes the weight of a seated occupant borne by the ischial tuberosities and the residual weight of the posterior and thighs to be distributed optimally over the two seating assemblies, regardless of the occupant""s seated position. The combination also allows the muscles, tendons, and ligaments of the lower back, pelvic, and thigh areas to be exercised, improving fluid flow (e.g., blood circulation), alertness, flexibility, and inhibiting back pain.